I'm noticing something interesting my mining rig maintains a fairly solid daily income despite difficulty increases or price fluctuations. For you guys who have been mining for a longer time noticed the same thing?

If you're on deepbit I'd say that's almost impossible, there was a period of unluckiness that deepbit hit, where the 24hr average block time was 23 minutes per block, right now it's 15 minutes per block (with 400Ghash/sec less).

Now the above is flawed in that the rig will have mined more BTC earlier on and that BTC will now be worth more. I need to sit down and figure out the daily ZAR (local currency) payment for each specific day.